The present invention relates to suppression of audible noises generated by mechanical components and, in particular, to suppression of noises generated by automotive vehicle engine components that are fabricated from metal or polymeric materials.
In the most recent three decades there has been a major push to increase the fuel economy of automotive vehicles. One technical trend to increase automotive fuel economy is to provide port, fuel-injected V6 or in-line, four-cylinder engines instead of the previously popular carbureted V8 engines. Another technical trend is to make the vehicle lighter. An excellent example of an automotive component that has been made lighter is the engine. Engine blocks are now typically fabricated from cast aluminum rather than prior cast iron. Additionally, many components such as the intake manifold, valve covers and oil pan are now formed from polymeric materials such as plastics which can withstand high temperatures and which can be injected or blow molded.
Polymeric manifolds have several advantages over prior cast aluminum or iron intake manifolds. Polymeric manifolds do not require as much finish machining or deburring and they also enhance the energy efficiency of the vehicle because they are lighter than their prior metallic counterparts. Polymeric manifolds can also be formed for production vehicles with smoother inner surfaces providing greater control of the incoming airflow and an improved volumetric efficiency of the engine.
However, polymeric manifolds have certain disadvantages. One disadvantage is that they have a tendency to be more susceptible to forced vibration than aluminum or cast iron manifolds. Accordingly, the use of polymeric materials has resulted in manifolds with undesirable noise characteristics, which is particularly disturbing on a premium vehicle where noise reduction is expected. Other polymeric engine components with relatively large flat surfaces have the same potential noise disadvantage.
It is desirable to provide an arrangement and method of utilization of a mechanical component (especially an engine component) subject to induced vibration (a generator of noise), that can be fabricated from a polymeric material and still have the desired acoustic damping characteristics of prior mechanical components fabricated from metallic material.
In a preferred embodiment, the present invention brings forth an automotive engine component such as an intake manifold which is fabricated from a polymeric material such as a fiber reinforced resin plastic. The component body has a panel portion on its exterior surface. Projecting from the panel portion are parallel spaced dual linear first and third projectors. Parallel spaced away from the panel portion is a sonic containment plate. The sonic containment plate on a side toward the main body of the intake manifold has a series of second linear projectors with angled surfaces that are received between the spacing of first and third projectors on the intake manifold. Both the containment plate and the manifold panel portion have interlocking hook members to allow the containment plate to have a flexible snap fit sealed connection to the main body of the intake manifold along the perimeter of the containment plate.
The first and third projectors are preferably placed on the portion of the manifold having maximum vibratory amplitude, and will accordingly stiffen the manifold, while retaining the weight advantage of the polymeric material over prior metal manifolds. The stiffening provided by the projectors will help reduce or eliminate lower frequency modes of vibration. Additionally, the containment plate defines an enclosed space which contains the air set forth in motion by the vibration of the manifold. The containment plate is therefore a barrier to sound transmission.
The flexible snap fit connection of the containment plate and the interference fit frictional engagement of the first and third projectors connected to the manifold body and the second projectors connected to the containment plate provide frictional damping to attenuate any vibratory energy (noise) generated by the intake manifold. Accordingly, less vibration is transmitted to the air surrounding the intake manifold.
Damping of a component can be obtained by one of four means: internal losses in a material, added viscoelastic material layers, added mechanism, e.g., tuned mass dampers, or microslip in joints. The latter is actually what provides most damping in most machines. However, it is the most difficult to characterize and control.
It is an advantage of the present invention to provide an acoustic suppression arrangement for a component that undergoes induced vibration.
It is an advantage of the present invention to provide damping by creating joints between a panel portion of a component and a containment plate that are springloaded by snap-fit connections, whereby the snap-fit connections elastically preload the joint to provide constant joint preload, required for consistent damping properties, independent of age and temperature.